iBook ATI and kernel compatibilty 6.16 kernel

Hi,

Working:
6.5.0-5-powerpc
6.12.6-powerpc
6.12.25-powerpc
  6.12.38-1 (2025-07-16) ppc GNU/Linux

6.15.1-1~exp1 (2025-06-05) boots with framebuffer and X11 (but has some 
other strange issues)
6.15.4-1~exp1 (2025-06-28) boots, some issues as above

Fails partially:
6.16-rc7-powerpc
Fails to boot: I see a kernel panic about unable being to open root, it 
doesn't find the root device.
The error message though is printed in the correct framebuffer, gray 
over black, so it already "switched" to it

Boots with errors:
6.16.3+deb14-powerpc
-> first time it booted to login and console, but there were 
non-blocking errors-
-> several reboots went fine when I saw a message saying
[  308.817803] ------------[ cut here ]------------
[  308.818079] UBSAN: shift-out-of-bounds in 
/build/reproducible-path/linux-6.16.3/arch/powerpc/net/bpf_jit_comp32.c:589:27
[  308.818280] shift exponent 32 is too large for 32-bit type 'int'
[  308.818411] CPU: 0 UID: 103 PID: 721 Comm: sshd-auth Not tainted 
6.16.3+deb14-powerpc #1 PREEMPTLAZY  Debian 6.16.3-1
[  308.818610] Hardware name: PowerBook2,1 740/750 0x88300 PowerMac
[  308.818728] Call Trace:
[  308.818794] [ccce99e0] [c0d93240] dump_stack_lvl+0x50/0x78 (unreliable)
[  308.818994] [ccce9a00] [c07ef3f4] ubsan_epilogue+0x10/0x40
[  308.819152] [ccce9a10] [c07eef98] 
__ubsan_handle_shift_out_of_bounds+0x17c/0x238
[  308.819315] [ccce9a90] [c0075d84] bpf_jit_build_body+0x4d74/0x4fd4
[  308.819467] [ccce9b40] [c006fc58] bpf_int_jit_compile+0x35c/0x5b4
[  308.819605] [ccce9bf0] [c024cd70] bpf_prog_select_runtime+0x1e0/0x2c4
[  308.819778] [ccce9c20] [c0b1d268] bpf_prepare_filter+0x5f0/0x794
[  308.819929] [ccce9c70] [c0b1d5d0] bpf_prog_create_from_user+0xe8/0x158
[  308.820073] [ccce9ca0] [c01bc678] do_seccomp+0x308/0xbb0
[  308.820207] [ccce9cf0] [c00aeb5c] sys_prctl+0x51c/0xa64
[  308.820339] [ccce9d40] [c0015500] system_call_exception+0xa0/0x120
[  308.820495] [ccce9f30] [c00211ac] ret_from_syscall+0x0/0x2c
[  308.820634] ---- interrupt: c00 at 0xa76f3318


Freezes during boot:
6.16.9+deb14-powerpc
... not anymore! it behaves like the kernel above. Boots, console, 
windows but issues those dumps stacks like 6.16.3

Right now I was able to have a full "apt-get upgrade".

After all this updating, installing kernels, testing, rebooting, 
updating packages and regenerating kernel and img seems to have made it 
working (before, I tested several times and it always froze and was not 
available to network.

So somehow there was a dependance from userland. Still situation is not 
perfect, but far better than a freeze.

People having issues on PowerBook G3 can confirm they have upgraded 
everything?

Riccardo